As of a year ago, at UVa, Dean J. said the admissions office didn’t track whether a student visited or not. She said they only added a sign-in sheet at the admissions office because so many visiting parents insisted that they had to be able to to sign in.
However, there are many other colleges that do carefully track “student interest,” because they are trying to lower their admit rates and increase their yield rates among admitted students. Those are often the same colleges that really push binding early decisions (which I hate). For those schools, unless you live far away, you should try to do an official admissions tour prior to an admissions decision.
At UVa, if you live far away and only have time for one visit, it is much better to do it during an admitted student day. You will receive much more useful information than on the standard admission tour, which wastes too much time on secret societies .Moreover, you lower the risk of a student really falling in love with UVa during the visit and then not getting admitted. It is better to fall in love with the place after an offer of admission.